Muscle Flashcards
What is the shape of skeletal muscle cells?
Elongated cells containing great number of cytoplasmic filaments
Where does all muscular tissue come from?
Hows does differentiation occur?
Medoserm
Differentiation occurs mainly by a process of cell lengthening and synthesis of myofibrillar proteins
→ Skeletal + Cardiac muscles come from Myotome (paraxial mesoderm)
→ Smooth muscle comes from mesenchymal cells
What are the 3 types of muscular fibers?
- Skeletal Striated muscle fibers
- Cardiac muscle fibers
- Smooth muscle fibers
How do A lines and I lines apprear (dark/pale)?
A line → darker
I line → paler
What are satellite cells?
Stem cells
- Only in skeletal striated muscle
Between the basement membrane and sarcolemma of striated muscle cells
- Role in tissue repair
- When needed, extra nuclei can be recruited from satellitle cells by mitotic division → 1 nucleus passing into the sarcoplasm
What are the characteristics of the nuclei of the different muscle fibers?
Skeletal striated muscle fibers nuclei:
- Multinucleated, in periphery
Cardiac muscle fibers’ nuclei:
- Centrally located nucleus
Smooth muscle fibers’ nuclei:
- Centrally located nucleus → from longitudinal section, looks as wide as the cell
- Cork screw shape
Why are smooth muscle not striated?
No myofibrils, intracellular structure made with actin
What is hypertrophy? Where does it occur?
Increase in muscle fiber size due to synthesis of myofibrils + myoglobin
Occurs only in striated muscles:
- Normal in skeletal muscles
- Abnormal in cardiac muscles (means the heart is not pumping efficiently)
What is Hyperplasia? Where does it occur?
Increase in number of muscle fibers
→ Normal in smooth muscle (uterine wall during pregnancy)
What are the speed of contraction different types of muscles?
Voluntary/Involuntary?
Smooth Muscle: contraction is slow, NOT voluntary control
Striated Skeletal Muscle: contraction is quick/forceful, Voluntary control
Striated Cardiac Muscle: contraction is NOT voluntary, vigorous and rhythmic
What is the role of tendons at both ends of the muscle?
Where are they at the level of the muscle?
Tendon = CT that acts as a mechanical transducer to transfer the forces generated by the contracting muscle cells to the bones
Tendons fuse with the Epimysium (Type I collagen) surrounding the muscle
Tendon = dense regular
Epimysium = dense irregular
What is the structure of a sarcomere?
Delimited by 2 Z-lines
Thin actin filament are attached to Z-lines and go towards the
Thick myosin filaments attached to M-line
What defines the pseudo band H ?
*inside the A band
It is the section both side of the M-line where the thin filaments don’t reach
If cut a cross section through the H pseudo-band, only see only Thick filaments
How many thick and thin filaments are in each myofibril?
3000 thin filaments
1500 thick filaments
What are the dimensions of muscle fibers?
1-40 mm (length) x 10-100 um (width)
How many myofibrils are in a muscle fiber?
up to 1500 myofibrils (1-2um diameter)
What do you see when you cut a cross section through the A band? I band?
A band → Actin (thin) and Myosin (thick) filaments (darker)
I band → actin filaments only (pale)
What defines the sarcomere?
It is the smallest repetitive subunit of the contratile apparatus
Extends from Z line to Z line (2-3 um)
What protein forms the Z line?
a-actinin → actin filaments bind to it (anchor)